1. Field of the Invention
The field of art to which this invention pertains is solids-vapors separation and more particularly the relationship between such separation and hydrocarbon processing. Specifically this invention relates to a fluidized catalytic cracking process in which the catalyst and oil are contacted for a certain period of time in a riser reaction zone and thereafter separated in a disengagement zone.
2. Prior Art
The prior art which is relevant to this invention can be found in classes covering fluidized conversion processing, and in particular fluidized catalytic cracking.
It is known in the art, that in certain instances, it is desired to substantially reduce the catalyst-oil contact times. Specifically, refiners have utilized riser cracking processes to eliminate the possibility of harmful secondary reactions which cause degradation of product quality. The solutions presented as can be seen in the patent art have centered around the use of cyclones connected to risers and the use of the so-called "quick quench" risers in which the riser outlets are designed or positioned so as to effect as rapidly and thoroughly as possible disengagement of the oil vapors from the catalyst. Examples of such patent art are U.S. Pat. Nos. 3,785,962 to Conner et al; 4,097,243 to Bartholic; 4,219,407 to Haddad et al; 4,295,961 to Fahrig et al; and 4,313,910 to Hubertus et al.
A recurring theme in the above patent art is for the vapor-particle stream flowing upward in the vertical riser to impinge on a surface opposing the upward flow and to be subjected to a 180.degree. change in direction followed by discharge downward into a disengagement zone comprising a cylindrical chamber. The impinging surface may form a "T" shape with the riser with the flow splitting and flowing into opposite arms of the T and each arm of the T discharging downward.
The latter of the above references show the impinging surface to be a downwardly sloping curved surface or dual sloping curved surfaces forming a modified T shape with the riser which causes an abrupt change in direction of the riser stream from vertical upflow to horizontal flow and then to downflow thereby establishing a centrifugal movement of particle flow which concentrates the particles on the upper side of the surface. The particles and vapors are thus at least partially centrifugally separated and released into a disengagement space in which the vapors return upward and flow out through cyclonic separators while the particles fall into a dense bed at the bottom of the disengagement zone. There is still, in the prior art designs, a degree of undesirable contact and remixing of the particles and vapors in the disengagement zone.
I have discovered a modification to the above downward sloping impinging surface or surfaces which has an amazing positive effect on the disengagement efficiency.